Selective halogenation of hydrocarbons

ABSTRACT

THE SELECTIVE MONO-HALOGENATION OF SATURATED HYDROCARBONS IS EFFECTED BY CHARGING A SATURATED HYDROCARBON AND A HALOGENATING AGENT TO A THERMAL DIFFUSION ZONE IN WHICH OPPOSING WALLS OF THE ZONE ARE MAINTAINED AT A TEMPERATURE DIFFERENTIAL FROM ABOUT 100* TO ABOUT 200*C. THE HYDROCARBON AND HALOGENATING AGENT WILL REACT THEREIN TO FORM MONO- AND POLY-HALOGENATED HYDROCARBONS. THE MONO-HALOGENATED HYDROCARBON WILL BE REMOVED FROM AN INTERMEDIATE POINT IN THE ZONE WHILE THE POLY-HALOGENATED HYDROCARBON WILL BE REMOVED FROM A LOWER PORTION OF THE ZONE.

g- 10, 1971 H. s. BLOCH SELECTIVE HALOGENATION OF HYDROCARBONS FiledNOV. 13, 1967 United States Patent @flice 3,598,876 Patented Aug. 10,1971 3,598,876 SELECTIVE HALOGENATION F HYDROCARBONS Herman S. Bloch,Skokie, 111., assignor to Universal Oil Products Company, Des Plaines,Ill. Continuation-impart of application Ser. No. 411,071, Nov. 13, 1964.This application Nov. 13, 1967, Ser. No. 684,595

Int. Cl. C07c 17/10 US. Cl. 260-660 Claims ABSTRACT OF THE DISCLOSUREThe selective mono-halogenation of saturated hydrocarbons is effected bycharging a saturated hydrocarbon and a halogenating agent to a thermaldiffusion zone in which opposing walls of the zone are maintained at atemperature differential from about 100 to about 200 C. The hydrocarbonand halogenating agent will react therein to form monoandpoly-halogenated hydrocarbons. The mono-halogenated hydrocarbon will beremoved from an intermediate point in the zone while thepoly-halogenated hydrocarbon will be removed from a lower portion of thezone.

This application is a continuation-in-part of my co-pending applicationSer. No. 411,071, filed Nov. 13, 1964, now abandoned.

This invention relates to a process for the halogenation ofhydrocarbons, and particularly to a process for the halogenation ofparafiinic hydrocarbons. More specifically, the invention is concernedwith a process for the selective mono-halogenation of paraffinichydrocarbons.

In many chemical processes or reactions a particularly desirablestarting material comprises a mono-halogenated hydrocarbon. A specificexample of one of these processes is the preparation of detergents.Heretofore, detergents comprising long-chain alkylaromatic sulfonateshave been prepared and used as such. However, many of these longchainalkyl substituents were highly branched in configuration. The increasinguse of detergents of this type has resulted in contamination orpollution of many streams, rivers, lakes, etc., inasmuch as it has nowbeen discovered that detergents of this type are non-biodegradable. Inthis respect the sight of streams, rivers, etc., containing largeamounts of foam has become increasingly prevalent. This may result in acontamination of the water supply for many cities or towns which dependupon these rivers or streams as a source of water supply.

In order to combat this disadvantage, detergents which are prepared nowand in the future must, of necessity, be biodegradable in nature. Thesebiodegradable detergents must contain long-chain alkyl substituentswhich are straight-chain in configuration or which may contain a minimumamount of branching, said branching preferably comprising no more thanmethyl radicals. This straightchain configuration of the alkyl chainwill permit the organisms which destroy the detergents to, in effect,eat their way up the chain thereby destroying the molecule and allowingthe detergent to be assimilated in the water without the concurrentproduction of undesired and lasting foam or suds.

A particular source of relatively straight-chain alkyl radicals whichmay be utilized as a starting material for the preparation ofbiodegradable detergents comprises the normal aliphatic paraflinichydrocarbons which are separated from isomeric mixtures of normal andbranched chain paraffius by any means well known in the art, oneparticular means of separation being the use of molecular sieves. Theselong-chain aliphatic paraflinic hydrocarbons,

preferably ranging from about 9 to about 15 carbon atoms in length,will, after treatment thereof, be utilized as alkylating agents forbenzene or toluene to prepare biodegradable detergents. Thispretreatment of the aliphatic paraffinic hydrocarbon may, if so desired,be effected by halogenating the paraflins whereby an alkyl halide ofdesired configuration is produced. Another type of treatment is topartially oxidize the aliphatic paraflinic hydrocarbon to produce analcohol, either the alcohol or halide then being utilized as thealkylating agent. It is preferable that the alkyl halide which is to beused as an alkylating agent contain only one halogen substituent so thatthe resulting alkylaromatic compound contain the aliphatic substituentin a straight chain. The position of the halogen radical in the chain isrelatively immaterial, said halogen substituent being on either the 1-,2- or 3-carbon atom or other carbon atoms in the chain. While theforegoing discussion is concerned mainly with the halogenation of arelatively longchain aliphatic paraflinic hydrocarbon, other types ofhydrocarbons such as cycloparaffinic hydrocarbons and aromatichydrocarbons which also may contain an alkyl sidechain are also subjectto mono-halogenation according to the process of this invention.

Heretofore, the prior art has shown the chlorination of gaseoushydrocarbon such as methane while passing the reactants between wallswhich may be maintained at different temperatures. The gaseoushydrocarbon and chlorine are passed through the reactor upwardly fromthe bottom thereof and the entire reaction products are removed from thetop portion of said reactor. However, merely maintaining the walls ofthe reactor at different temperatures is not sufficient in and of itselfto provide a thermal diffusion separation zone. In contradistinction tothis prior art, the present invention is concerned with a process forhalogenating paraflinic hydrocarbons in a liquid phase and thereafterseparating the mono-halogenated paraffins from the poly-halogenatedhydrocarbon within the thermal diffusion zone, said halogenation andseparation of the different products being effected in a single stageoperation. One advantage of effecting the halogenation according to theprocess of the present invention includes a high selectivity toward themono-halogenated product, as against the less desired poly-halogenatedproduct, as well as the direct drawoff of the relatively pure product.When utilizing the process of the present invention it is preferred tocharge the saturated hydrocarbon, and particularly a paraffinichydrocarbon of the type hereinafter set forth in greater detail, and thehalogenating :agent to the top of the thermal diffusion zone, and flowthe reacting mixture downwardly therethrough while withdrawing themono-halogenated product from an intermediate point and the undesiredpoly-halogenated product from a lower portion of the zone.

It is therefore an object of this invention to provide a process for theselective halogenation of saturated hydrocarbons.

A further object of this invention is to provide a process for theselective mono-halogenation of paraffinic hydrocarbons utilizing athermal diffusion apparatus.

In a broad aspect, one embodiment of this invention resides in a processfor halogenating a paraffiuic hydrocarbon containing from about 4 toabout 20 carbon atoms which comprises introducing said hydrocarbon and ahalogenating agent comprising chlorine or bromine into the upper portionof a thermal diffusion zone having opposing walls maintained atdifferent temperatures, the hotter wall being at a temperature in therange of from about 50 C. to about 200 C. and the cooler wall being at alower temperature in the range of from about 0 to about 50 C., thetemperature differential between said hotter wall and said cooler wallbeing from about 50 C. to about 200 C., reacting said hydrocarbon andsaid halogenating agent while passing downwardly between said walls,thereby forming monoand poly-halogenated hydrocarbons, separatingmono-halogenated hydrocar bons from poly-halogenated hydrocarbon withinsaid thermal diffusion zone and withdrawing the former from anintermediate point in the height of said zone and withdrawing separatedpoly-halogenated hydrocarbons from the lower portion of said zone.

A specific embodiment of this invention is found in a process for theselective mono-bromination of dodecane which comprises introducingdodecane and bromine to the upper portion of a thermal diffusion zonehaving opposing walls maintained at different temperatures, the hotterwall being at a temperature in the range of from about 50 C. to about200 C. and the cooler wall being at a temperature in the range of fromabout C. to about 30 C., reacting said dodecane and bromine whilepassing the mixture downwardly between said walls, thereby formingmono-bromododecane and poly-bromododecane, separating mono-bromododecanefrom polybromododecane within the thermal diffusion zone, withdrawingthe mono-bromododecane from an intermediate point in the height of saidzone, and thereafter withdrawing separated poly-bromododecane from thelower portion of said zone.

Other objects and embodiments will be found in the following furtherdetailed description of the present invention.

As hereinbefore set forth the present invention is concerned with aprocess for the selective mono-halogenation of saturated hydrocarbonsand particularly paraffinic hydrocarbons.

In the halogenation of hydrocarbons, and particularly in the preparationof sec-alkyl bromides from n-paraffins, some difficulty has beenexperienced in obtaining the selective mono-halogenation ormono-bromination and subsequently separating mono-brominated productfrom diand poly-brominated product, the difficulty being attributed tothe thermal instability of the bromo compounds. The process of thepresent invention will overcome the difficulty by permitting highselectivity as well as a relatively easy separation of the varioushalogenated, and especially brominated, species without thedecomposition of the halogenated products. In addition, the process ofthis invention will permit a ready separation of the various specieseven if the hydrocarbon feed consists of several homologs of such aboiling range that the highest boiling hydrocarbons overlap in boilingpoint the lowest boiling mono-halogenated products. As hereinbefore setforth, I now propose to halogenate, and specifically brominate,hydrocarbons such as n-parafiins of relatively long-chainedconfiguration in a thermal diffusion apparatus. This apparatus, in oneembodiment thereof, consists of a relatively narrow, annular spacebetween two walls which are heat-conductive in nature and which areprovided with means for maintaining heat differential or gradientbetween said walls. The annular space or slit widths between the closelyspaced parallel walls are extremely narrow. The space or slit width mayrange in size from about 0.01 inch to about 0.25 inch, the opposed facesof the vertical, liquid-impervious walls being smooth and spacedsubstantially equidistantly from one another to form the aforementionedslit. The temperature controlling means whereby a heat differential maybe maintained between the walls will comprise means for heating onewall, which will hereinafter be designated by the term hot wall andmeans for cooling the opposite wall, hereinafter referred to as the coolwall. The aforementioned heating and cooling means which are utilized inthe apparatus required to effect the process of the present inventionwill comprise those which are well known in the art and may consist ofelectrical wires, tubes for hot gases, water pipes for either hot orcold water, or any other known heat transfer means. The thermaldiffusion apparatus, which will hereinafter be described in greaterdetail, will also contain means such as ports, inlets, outlets, etc.communicating with the slit or annular space whereby the hydrocarbonfeed and the halogenation agent may be charged to the apparatus as wellas means for withdrawing the various halogenated products including themono-halogenated hydrocarbon and the polyhalogenated hydrocarbon.

Due to the difference in boiling points and molecular weights, if amixture of paraffinic hydrocarbons, monohaloparafl'ins andpoly-haloparaffins is fed to a thermal diffusion unit, the mixture isreadily separated into three layered products. The paraffins will befound in the upper portion of the unit, the mono-haloparaffins at anintermediate level, while the poly-haloparafiins are at the bottomthereof. Therefore, it is readily apparent that the halogenation, andparticularly bromination, of hydrocarbons can be effected by feedingparaffinic hydrocarbons to the upper portion of a thermal diffusionunit, also feeding the halogenating agent to the upper portion, andsubsequently withdrawing mono-halogenated paraffins from an intermediatelevel and the poly-haloparaffins from a lower level. By utilizinghalogenating agents such as bromine and chlorine and controlling therate of feed of the halogenating agent so that essentially all of itreacts in the top portion of the unit, while the halogenated paraffinstravel downward, there results a minimum of poly-halogenation and agreater percentage of mono-halo products will be achieved thereby. Thishigh selectivity of mono-halohydrocarbon formation will be especiallyadvantageous when preparing long-chain alkyl monohalides for use asalkylating agents in the preparation of biodegradable detergents.

The present invention will be further illustrated with reference to theaccompanying drawing which illustrates a simplified thermal diffusionunit which may be utilized to effect mono-halogenation of parafiinichydrocarbons according to the process of the present invention. Variousvalves, condensers, pumps, controllers, etc. have been eliminated as notbeing essential to the complete understanding of the present invention.The utilization of these, as well as other similar appurtenances, willbecome obvious as the drawing is described.

Referring now to the drawing, a hydrocarbon, either ahphatic paraffinic,cycloaliphatic paraffinic or aromatic 1n nature, the preferred chargecomprising an aliphatic parafiinic hydrocarbon containing from about 4to about 20 carbon atoms, is charged to a thermal diffusion unit 1through line 2 into the upper portion of said unit. A halogenating agentcomprising elemental bromine, elemental chlorine, etc. is also chargedto the upper portion of thermal diffusion unit 1 through line 3. Thethermal diffusion unit in one embodiment thereof comprises a cell whichcontains at least two liquid-impervious walls made of heat-conductingmaterial, said walls being closely spaced so as to form a relativelynarrow space between said walls. As has been previously discussed thenarrow space between said walls, in one embodiment hereof, will comprisea vertical slit having a thickness of from about 0.01 inch to about 0.25inch. These walls comprise a hot wall 4 and a cold wall 5. Each wall isprovided with heat transfer means of the type hereinbefore set forth,said means being capable of maintaining a temperature differential orgradient between the faces of said walls. As hereinbefore set forth, thehydrocarbon and the halogenating agent along with diluent gas for thehalogenating agent, if one is desired, are continuously charged to theupper portion of unit 1. Unit 1 is also provided with line 6 whereinhydrogen bromide or hydrogen chloride which is formed during thehalogenation may be withdrawn along with any diluent gas which has beenemployed. The mono-halohydrocarbon is continuously withdrawn from anintermediate portion of unit 1 through line 7. While only one line hasbeen illustrated, it is contemplated within the scope of this inventionthat several lines for withdrawal of the mono-haloparaflin may beemployed at rvarious positions adjacent to the intermediate portion ofthe unit. If dior poly-halohydrocarbons are formed, they will flow in adownward manner to the bottom portion of unit 1 where they will bewithdrawn from the unit through line 8. Likewise, in the drawing onlyone poly-halohydrocarbon withdrawal line has been illustrated, althoughmore than one line may be utilized. It is to be understood that thedrawing illustrates only one form of a thermal diffusion apparatus whichmay be used and that it is contemplated within the scope of thisinvention that other types of apparatus may be used and said apparatuseswhich are tubular in shape or which consist of a multiple tube type ofthermal diffusion apparatus may also be used. In particular, all

halogenated products may be withdrawn from a bottom drawoff point 8 (7being not used) and the effluent passed to a second thermal diffusionunit whence mono-brominated products are withdrawn from the bottom, thisseries of units therefore being equivalent to the single unit withmultiple withdrawal points illustrated herein.

The heat-conductive walls which make up a portion of this apparatus maybe of any suitable material, the only limitation being that the materialbe inert to the reactants and capable of being heated or cooled byexternal means. Suitable metals which may be used include stainlesssteel, copper, brass, or other alloys which are heat conductive, as wellas non-metallic materials such as glass, porcelain, and the like.

As hereinbefore set forth, in the preferred embodiment of this inventionboth walls are provided with heat transfer means which are capable ofmaintaining a temperature gradient between the inner faces of the walls.It is contemplated within the scope of this invention that thetemperature of the hot wall should not be above the boiling ordecomposition point of the hydrocarbons which are introduced into theunit at the pressure used, and, likewise, the temperature of the coldwall should not be below the freezing point or crystallization point ofthe hydrocarbons as well as the mono-halogenated and polyhalogenatedhydrocarbons. For example, the temperature of the hot wall may bemaintained in a range of from about 50 up to about 200 C., dependingupon the particular hydrocarbon which is to undergo halogenation. At thesame time, the temperature of the cold wall is maintained at arelatively low temperature in the range of from about 0 up to about 50C., the preferred range being from about 0 to about 30 C., thetemperature gradient preferably being as much as about 50 C., to about200 C. Although it is preferred to operate the process under atmosphericpressure it is also contemplated within the scope of this invention thatthe selective halogenation of the parafiinic hydrocarbon be effectedunder superatmospheric conditions ranging from 2 up to 50 atmospheres ormore, the pressure being that which is sufficient to maintain a majorportion of the reactions in a liquid phase, in order that the paraffinichydrocarbon be selectively halogenated and separated to recover thedesired mono-halogenated hydrocarbon from the polyhalogenatedhydrocarbon.

Examples of saturated hydrocarbons, and particularly parafiinichydrocarbons, which may be subjected to the selective halogenationprocess of the present invention comprise those which preferably containfrom about 4 to about carbon atoms in length and may be eitherstraight-chain or branched-chain in configuration, the straight-chainparafiins being preferred. Specific examples of these compounds willinclude n-butane, n-pentane, nhexane, n-heptane, n-octane, n-nonane,n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane,n-pent-adecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane,n-eicosane, and branched-chain isomers thereof.

By utilizing a continuous method of operation it is possible to achievea high selectivity of mono-halogenation, and particularlymono-bromination, and, in addition,

it is easy to separate the different products in relatively pureform.This ease of separation and selectivity will offer a distinct advantageover the former methods which have been used in order to obtainmono-halogenated hydrocarbons. This continuous process is simple in forminasmuch as the parafiins and the halogenating agent can be set into theupper portion of the cell while withdrawing the mono-halogenated productfrom an intermediate level and the diand poly-halides from a lowerlevel. Inasmuch as the halogenating agent, preferably an elementalhalogen, will normally travel upwardly as it reacts in the paraffiniczone and the halogenated parafiins will travel downwardly, a minimum ofhalogenation of the haloparaffins will be achieved in such a process andtherefore, as hereinbefore set forth, a high selectivity ofmono-halogenation will be achieved. Another advantage which will befound by utilizing the process of the present invention is that it ispossible to use a fairly wide boiling range of feed stocks as startingmaterials with the concurrent ease of separation of halogenated productsthus adding another advantage over the methods now in use to obtain thedesired products.

The following examples are given to illustrate the process of thepresent invention which, however, are not intended to limit thegenerally broad scope of the present invention in strict accordancetherewith.

EXAMPLE I A thermal diffusion apparatus comprising two liquidimperviousstationary walls of heat-conductive material spaced about 0.05 inchapart is utilized in this experiment. One wall is provided with heatingmeans while the other wall is provided with cooling means. The heatingmeans comprise conduits through which hot gases are fed, while thecooling means comprise conduits through which cold water flows. The hotwall is maintained at a temperature of about 170 C., while the cold wallis maintained at a temperature of about 20 C. The apparatus is alsoprovided with outlet means at an intermediate portion and a lowerportion thereof. A hydrocarbon cut comprising ndodecane derived from ahydrocarbon mixture which was subjected to separation utilizingmolecular sieves is charged to the thermal diffusion apparatus throughone inlet means in the upper portion of the apparatus, at a rate equalto the rate of liquid withdrawal from the reactor. Elemental bromine isalso charged to the apparatus through another inlet means in the upperportion thereof. The dodecane is present in the thermal diifusionapparatus in a mole ratio of about 15 moles of dodecane per mole ofbromine fed per hour. The mono-bromododecane is continuously withdrawnfrom the outlet means in the intermediate portion of the apparatus,while any diand poly-bromododecanes which are formed are withdrawn fromthe lower portion of the apparatus. The hydrogen bromide which is formedin the upper portion of the apparatus is withdrawn from the top of saidapparatus and recovered.

EXAMPLE II In this example a thermal diffusion apparatus is utilizedsimilar to that described in Example I above, but the walls of the zoneare maintained at a distance apart of about 0.15 inch. To this apparatusis charged a stream of undecane which is purified before admission intosaid apparatus by admixture with sulfuric acid followed by heating andcooling. The two layers are separated, the undecane is washed withwater, 10% sodium hydroxide solution and again with water. Followingthis, the hydrocarbon is dried by passage over sodium sulfate andthereafter charged to the apparatus. The bromine is also purified bydistillation to remove any metals which may be present and is thencharged to the apparatus. The hot wall of the apparatus is maintained ata temperature of about 160 C., while the cold wall is maintained at atemperature of about 15 C., thereby maintaining a temperature gra dientof about C., throughout the length of the ap- 7 paratus. Themonobromoundecane is continuously withdrawn from the intermediateportion of the apparatus and purified by conventional means, while anypolybromoundecanes which may have'formed are withdrawn from the bottomportion of the apparatus.

EXAMPLE III In this example a thermal diffusion apparatus compris ingtwo liquid-impervious stationary walls are spaced at a distance of about0.15 inch apart. The hot wall of the thermal diffusion apparatus ismaintained at a temperature of about 150 C. while the cooled wall of theapparatus is maintained at a temperature of about C. The charge stock inthis experiment comprises decane which is previously passed through asilica gel column, collected in a flask, purged of air by a steadystream of nitrogen and stored under a nitrogen blanket until used.Bromine along with nitrogen which acts as a diluent gas is chargedthrough the apparatus through inlet means at the upper portion thereofin such an amount that the mole ratio of decane to bromine is aboutmoles of decane per mole of bromine fed per hour. The monobromodecane iscontinuously withdrawn through outlet means at an intermediate portionof the apparatus, while poly-boromdecanes, to the extent formed, arewithdrawn through outlet means at a lower portion of the apparatus. Inaddition, hydrogen bromide which is formed during the bromination of thedecane and diluent gas comprising nitrogen are continuously withdrawnfrom the top of the apparatus.

I claim as my invention:

1. A process for halogenating a paraffinic hydrocarbon containing from 4to 20 carbon atoms which comprises introducing said hydrocarbon and ahalogenating agent comprising chlorine or bromine into the upper portionof a thermal diffusion zone having opposing closely spaced verticalparallel walls maintained at different temperatures, the hotter wallbeing at a temperature in the range of from about 50 C. to about 200 C.and the cooler wall being at a lower temperature in the range of fromabout 0 to about 50 C., the temperature differential between said hotterwall and said cooler wall being from about 50 C. to about 200 C.,reacting said hydrocarbon and said halogenating agent while passingdownwardly between said walls, thereby forming mono and poly-halogenatedhydrocarbons and hydrogen halide, removing said hydrogen halide from theupper portion of said thermal diffusion zone, separating by thermaldiifusion mono-h alo genated hydrocarbon from poly-halogenatedhydrocarbon within said thermaldiffusion zone and withdrawing saidmono-halogenated hydrocarbon from an intermediate point in the height ofsaid zone and withdrawing separated poly-halogenated hydrocarbons fromthe lower portion of said zone. i

2. The process as set forth in claim 1, further characterized in thatsaid halogenating agent is bromine. 3. The process as set forth in claim1, further characterized in that said halogenating agent is chlorine.

4. The process as set forth in claim 1, further characterized in thatsaid hotter wall is at a temperaturein the range of from about C. toabout 200 C. and said cooler wall is at a, temperature in the range offrom about 0 C. to about 30 C. i 5. The process as set forth in claim 1,further char acterized in that said hydrocarbon is a straight-chainparaffin containing from 10 to 20 carbon atoms. 6. The process as setforth in claim 5, furthercharacterized in that said hydrocarbon isdecane. 7. The process as set forth in claim 5, further characterized inthat said hydrocarbon is undecane. 8. The process as set forth in claim5, further char acterized in that said hydrocarbon is dodecane. 9. Theprocess as set forth in claim 5, further char acterized in that saidhydrocarbon is pentadecane.

10. The process of claim 1 wherein the opposing walls of said thermaldiffusion zone are spaced apart a distance of about 0.01 inch to about0.25 inch.

References Cited UNITED STATES PATENTS 2,168,260 8/1939 Heisel et al.260660X 2,898,384 8/1959 Viriot 260658 3,316,294 4/1967 Feighner260-662X FOREIGN PATENTS 378,873 8/1932 Great Britain 260-660 BERNARDHELFIN, Primary Examiner M. W. GLYNN, Assistant Examiner US. Cl. X.R.

